Gregorian to Julian Date

Ordinal Date (YYDDD)
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Full Ordinal Date (YYYYDDD)
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Day of Year
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Julian Day Number (JDN)
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Julian Date to Gregorian

Gregorian Date
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ISO Date
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Detected Year
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This calculator supports Ordinal Date format (YYDDD and YYYYDDD), often called a Julian Date in computing.


Use this Julian Date Calculator to convert a Gregorian calendar date and time into Julian Date (JD), Modified Julian Date (MJD), Julian Day Number, day of year and common YYDDD or YYYYDDD ordinal codes. You can also convert a Julian Date back to a UTC calendar date.

How to Use the Calculator

  1. Select a calendar date, time and whether it represents local time or UTC.
  2. Tap Calculate Julian Date to view JD, MJD and related formats.
  3. For reverse conversion, enter a JD and tap Convert JD to UTC.

Julian Date, MJD and Ordinal Date

Astronomical Julian Date is a continuous count of days and fractions beginning at noon in the Julian system. Modified Julian Date is calculated as JD minus 2400000.5, so its day starts at midnight. The compact YYDDD and YYYYDDD values are ordinal-date codes made from the year and day number within that year; they are different from astronomical JD.

This calculator uses the proleptic Gregorian calendar for its date input. Historical regions adopted the Gregorian calendar on different dates, so use specialist references when interpreting old civil records.

Frequently Asked Questions